The present invention relates to wind turbines, more specifically to a wind turbines with multiple straight blades around a substantially vertical axis and a collective blade-pitch control system therefor.
Wind turbines commonly known as windmills have been used to produce power via a mechanical shaft for thousands of years. Vertical axis windmills are probably among the oldest of all. Many various types of arrangements have been created in recent years. Some modifying the design, construction or assembly of the blades, or modifying the attachment system between the support struts and the blades, or also modifying the blade-pitch control system regulating the angular speed of the blades.
In the U.S. Pat. No. 1,835,018 to Darrieus entitled xe2x80x9cTurbine having its rotating shaft transverse to the flow of the currentxe2x80x9d and dated Dec. 8, 1931, the U.S. Pat. No. 4,299,537 to Evans entitled xe2x80x9cInterlinked variable-pitch blades for windmills and turbinesxe2x80x9d and dated Nov. 10, 1981, the U.S. Pat. No. 4,718,821 to Clancy entitled xe2x80x9cWindmill bladexe2x80x9d and dated Jan. 12, 1988, the U.S. Patent 5,057,696 to Thomas entitled xe2x80x9cVertical windmill with omnidirectional diffusionxe2x80x9d and dated Oct. 15, 1991, and the U.S. Pat. No. 5,126,584 to Ouellet entitled xe2x80x9cWindmillxe2x80x9d, no specific design features are given to reinforce the construction of the blades themselves, except in Ouellet where a shaft goes through the blades, and in Thomas where a shaft goes through the external vertical stator to protect from high winds but not specifically inside the airfoils. In those cases, however, there is no system permitting for example to have for each blade assembly a strong rod and a light and resistant blade surrounding the rod. In Thomas the system of airfoils basically has to be protected by the use of the complex stators. In most cases however, robust and strong construction of all of the blades may mean heavier blades.
Furthermore, heavy blades, and long blades will both be a cause for higher bending stresses due to the centrifugal forces being exerted on the blades during the rotation of the rotor, often resulting in added cost in the construction of the blades and the turbine rotor. In the case of Ouellet however, a bracing ring solidifies the shutters, but part of the shutters are fixed. In the case of Thomas, upper and lower support bars are included in the system, but they are inserted in-between the vertical stators, preventing the stators or blades to have relatively large length or height. Clancy and Evans also both show struts to attach the blades, but this is done on the outside of the blade, necessitating a more rigid blade than if the attachment was done on a structural member inside the blade for example.
On wind turbines, a relatively strong design focus is also given to the pitch control of the blades to regulate speed and/or power output of the rotor. Some have a system where pitch control is individually provided for each blade, such as in Clancy, which subjects each blade to cyclic fluctuations during each rotation due to the variation of aerodynamic pressures acting on the blade during its rotation and could result in greater wear and tear on the blades and increased maintenance costs.
The pitch control system is also sometimes collective such as in Darnieus, Evans, Thomas and Ouellet. In Darrieus"" invention, the pivoting blades are linked to an eccentric ring to give a possible oscillation on the blades when they are in rotation. This system is purely a blade pitch control system, as also in Evans"" invention. In both inventions, the force of the wind is furthermore inducing the pitch control (via a system of linkages at the top of the central vertical shaft in Evans"" case) as opposed to have the centrifugal forces acting in the pitch control.
In Thomas"" invention, the centrifugal forces act upon an arm pivoting about the strut. As such, the arm does not tend to rotate the disk, which is activated via a loose cable, which becomes tight as the arm extends outwards. Furthermore, the pitching of the blades is finally achieved through a system of cables and cam sliding in a rail attached to the blade. The collective blade-pitch control is not in this case provided by centrifugal forces that tend to turn the disc and arise from centrifugal forces acting on the unbalanced blades and connecting rods. Ouellet""s invention has a plurality of stationary and movable shutters arranged inside the rotor. Both previously mentioned inventions have a collective pitch control system requiring an elaborate mechanism including numerous cams and cables or toothed crown wheel and pinions.
It is therefore a general object of the present invention to provide a wind turbine device of the character described which obviates the above noted disadvantages.
Another object of the present invention is to provide a wind turbine device that provides a simple and effective collective blade-pitch control system induced by centrifugal forces to self-regulate the angular speed and/or power output of the rotor of the wind turbine.
A further object of the present invention is to provide a wind turbine device that provides a method of effective attachment of multiple retainer struts in order to limit the effects of centrifugal forces or bending stresses on the blades while keeping the blades"" maximum effectiveness.
Another object of the present invention is to provide a wind turbine device that gives simple design and structural modifications to strengthen and lighten turbine blades.
Another object of the present invention is to provide a wind turbine device that has a support structure easily adaptable to receive more than one rotor assembly depending on the required output power.
The present invention is directed to a wind turbine device of the vertical axis type that comprises:
a static support structure rotatably supporting a rotor assembly at its substantially vertical turbine drive shaft connected to a power generator member, the rotor assembly also includes;
a plurality of vertical blade members equally and circumferencially spaced apart from and parallel to said shaft, said blade members having a leading and a trailing edges, said blade members being vertically pivotally mounted at their top and bottom extremities and close to said leading edge to respective rigid horizontal support struts to allow for a variable pitch angle of said blade members from a neutral position with said blade member being essentially tangential to said shaft, each of said horizontal support struts being fixedly radially secured to said shaft;
a short horizontal arm secured at one end on respective of said blade members and substantially tangential to said shaft and secured at a second end to a first extremity of a respective rigid horizontal control rod;
a second extremity of each of said control rod is secured to a common control disc member rotatably mounted to said shaft; and
a control disc biasing member secured to said shaft and biasing said control disc member against any positive common angular pivoting change of said pitch angle of said blade members about their respective pivoting axis.
Preferably, the second end of each of said short horizontal arms includes an adjustable weight member to allow for specific calibration of said blade member of said wind turbine device.
Preferably, each of the blade members includes a shaped external body having a leading and a trailing edges and a center of aerodynamic pressure loads therebetween, and being longitudinally pivotally mounted onto a substantially vertical post member at said center of pressure loads, said vertical post member being rigidly secured to respective said horizontal support struts, said leading edge of said external body having said one end of said respective short arm being secured thereto.
Preferably, each of the blade members further includes at least one substantially horizontal intermediate retainer member fixedly secured to said shaft at a first extremity and rotatably secured to said vertical post member of said blade member at a second extremity, said intermediate retainer members being equally spaced a part along said external body between said respective horizontal support struts and parallel to the latter.
Preferably, each of the vertical post members is located inside said respective external body that is pivotally mounted thereon, said external body of said blade member having at least one corresponding small opening allowing said second extremity of said intermediate support member to reach said vertical post member and a substantial free pivoting of said external body around said vertical post member with said pitch angle varying between zero and +25 degrees from said neutral position.
Preferably, each of the vertical post members includes an inner tube rigidly secured to said respective horizontal support struts at its extremities and an outer tube coaxial to said inner tube and rotatably secured therealong, said outer tube being rigidly secured to said external body and of essentially a same length thereof, said outer tube also having at least one corresponding small opening allowing said second extremity of said intermediate support member to reach said inner tube and a substantial free pivoting of said outer tube around said inner tube with said pitch angle varying between zero and +25 degrees from said neutral position.
Preferably, the control disc member is a generally round disc with a radius relatively smaller than the distance separating each of said blade members from said shaft such that each of said control rods is substantially parallel to said corresponding support struts, and said control disc biasing member includes a transverse bar rigidly secured to said shaft and abutting at least one pair of biasing springs axially supported by said round disc, said biasing springs biasing said control disc member and said blade members into said neutral position thereby controlling rotational speed of said shaft at a pre-determined speed for said power generator member.
Preferably, the short horizontal arms, said control rods, said control disc member and said control disc biasing member are substantially at mid vertical distance between said respective horizontal support struts.